GitLab

* Top level Python module is now "openmm"

* Updated module names in examples

* Updated module names in documentation

* Updated module in CI scripts

* Added deprecation warning

* Improve vec3

* Added a ``__neg__`` operator overload so that -Vec3(1, 2, 3) returns
  the same thing as Vec3(-1, -2, -3)
* Derived Vec3 from namedtuple instead of tuple. This allows you to
  access the 3 elements of the vector by name. i.e., vec.x, vec.y, vec.z

* Make sure we use floating point division all the time.